The performance of CDMA systems is limited by multiple access interference (MAI). Among many interference cancellation schemes, successive interference cancellation (SIC) is highly desirable, due to its low complexity, high compatibility with existing systems and easy accommodation to strong error-correcting codes [A. J. Viterbi, “Very low rate convolutional codes for maximum theoretical performance of spread-spectrum multi-access channels,” IEEE J. Select Areas Commun. Vol. 8, pp. 641-649, May 1990]. However, unlike other detection techniques, SIC is sensitive to received power allocation. By providing channel state information (CSI) at the receiver and reliable feedback of power allocation from the receiver to the transmitter, we are able to integrate SIC with power control (PC), which can improve system capacity significantly.
For a system which aims to achieve comparable performance for all users, equal BER criterion is suitable for deriving the power allocation. As has been concluded in the literature, equal BER PC benefits SIC significantly by increasing the reliability of earlier detected users. Nevertheless, most of the work focused on (match filter) SIC (MF-SIC) [Viterbi op. cit.; G. Mazzini “Equal BER with successive interference cancellation DS-CDMA systems on AWGN and Ricean channels,” in Proc. ICCC PIMRC, July 1995, pp. 727-731; R. M. Buehrer, “Equal BER performance in linear successive interference cancellation for CDMA systems,” IEEE Trans. Commun., vol. 49, no. 7, pp 1250-1258, Jul. 2001]. With the increase of system load, in CDMA systems, the performance of MF degrades quickly, limiting the effectiveness of SIC. Therefore, it is meaningful to integrate PC with SIC for more powerful detection techniques, such as decorrelating and MMSE. For a given decision order, MMSE SIC (MMSE-SIC) maximizes all users' SIRs simultaneously [T. Guess, “Optimal sequences for CDMA with decision-feedback receivers,” IEEE Trans. Commun., vol., 49, pp. 886-900, Apr. 2003]. Therefore, in this invention we consider the equal BER PC algorithm for this optimal SIC receiver in quasi-synchronous uplink MC-CDMA.